Chapter 2: Atoms, Molecules and Water

Question 1

What is the difference between acid and base in respect to chemical formulas?

Answer 1

H+ (hydrogen ions) is a property of acids, and OH- (hydroxide ions) is a property of bases.

Question 2

What are the smallest units of matter?

Answer 2

atoms

Question 3

What charges do the three subatomic particles of an atom have, and where are they located?

Answer 3

Protons are positively charged, located in the nucleus. Neutrons are electrically neutral, located in the nucleus. Electrons are negatively charged, located in orbitals around the nucleus.

Question 4

T or F. Electrons and neutrons are present in equal numbers, giving the atom a no net charge.

Answer 4

False; electrons and PROTONS are present in equal numbers, giving the atom a no net charge.

Question 5

How are orbitals organized?

Answer 5

They are organized into electron shells; first shell contains one orbital (max of 2e-), whereas second shell contains 4 orbitals (max of 8e-)

Question 6

What are valence electrons?

Answer 6

electrons in the OUTERMOST shell; which can participate in the formation of chemical bonds

Question 7

What distinguishes one element from another?

Answer 7

the number of protons

Question 8

How do you know if two elements have similar properties?

Answer 8

Both elements are within the same column and have the same number of electrons in their valence shell

Question 9

How can you determine the atomic mass of an element?

Answer 9

Add the number of protons and neutrons. Ex: 5 protons and 4 neutrons; atomic mass=9.

Question 10

What are isotopes?

Answer 10

Elements that exist in different forms, that differ in the number of neutrons they contain.

Question 11

What elements make up 95% of an organisms’ mass?

Answer 11

oxygen, carbon, hydrogen, and nitrogen

Question 12

How do covalent bonds form?

Answer 12

They form when atoms share a pair of electrons.

Question 13

T or F. Covalent bond are weak bonds.

Answer 13

False; covalent bonds are STRONG bonds.

Question 14

How many covalent bonds can carbon form?

Answer 14

4

Question 15

What is electronegativity?

Answer 15

the ability of an atom to attract electrons

Question 16

In order to determine if a covalent bond is polar or non-polar, you must know the electronegativity of an atom. An atom is non-polar if the electrons are shared equally and have a difference in electronegativity that is greater than 0.4. An atom is polar if the electrons are shared unequally and the difference in electronegativity ranges from 0.4 -1.8. What are the important electronegativity’s of some atoms?

Answer 16

Na: sodium (0.93); H: hydrogen (2.20); C: carbon (2.55); N: nitrogen (3.04); Cl: chlorine (3.16); O: oxygen (3.44)

Na H C N Cl O

Question 17

Give some examples of non polar and polar molecules.

Answer 17

Non polar: C-C, C-H, O-Cl,
Polar: O-C, N-O, N-H, O-H

Question 18

How are hydrogen bonds formed?

Answer 18

They form between a hydrogen with a partial positive charge and another electronegative atom.

Question 19

T or F. Hydrogen bonds are represented with a dashed line in a model.

Answer 19

True.

Question 20

What are the properties shared by many chemical reactions that occur in cells?

Answer 20

1) They require a catalyst. 2) They require energy. 3) They tend to proceed toward equilibrium.

Question 21

Which molecules readily dissolve in water? And what is this property called?

Answer 21

Ions and polar molecules readily dissolve in water (due to the difference in electronegativity), and they are called HYDROPHILIC. (water loving)

Question 22

What characteristics describe hydrophobic molecules?

Answer 22

1) they contain many non polar covalent bonds, 2) they are relatively insoluble in water

Question 23

Briefly describe the characteristics of water in its three states: solid, liquid, and gas. Describe their motion, describe the speed of the hydrogen bond breakage, and explain whether or not they bond is more or less stable.

Answer 23

Ice: water molecules are less likely to move apart and the rate of hydrogen bond breakage SLOWS; therefore hydrogen bonds are MORE stable, and are packed into an orderly formation

Water: water molecules are in rapid motion; hydrogen bonds CONTINUALLY break and re-form; hydrogen bonds are LESS stable than the solid form

Gas: water molecules increase in motion; hydrogen bonds are broken MORE readily, and hydrogen bonds are EVEN LESS stable than the water form

Question 24

Briefly list the important functions of water.

Answer 24

Participates in chemical reactions, provides support, removes waste, uses evaporative cooling, cohesion and adhesion, surface tension, and lubrication.

Question 25

T or F. Acids contain the LOWEST proton concentration ( H+ < OH- ); they increase pH.

Answer 25

False. Acids contain the HIGHEST proton concentration, which means they have more H+ (hydrogen ions) than OH- (hydroxyl ions). As acid concentration increases (H+), pH decreases.

Example: Hydrochloric acid has a pH of 1, this means that it has the HIGHEST amount of H+ (hydrogen ions) possible.

Question 26

Label the parts of the atom.

Answer 26

Question 27

What is a molecule?

Answer 27

2 or more atoms that are bonded together (ex: N2 (nitrogen), O3 (ozone) )

Question 28

What is a compound?

Answer 28

A compound is a molecule composed of different elements. (ex: H2O (water), C6H12O6 (glucose) )

Question 29

How can you determine the atomic number of an atom?

Answer 29

The number of protons in an atom is its atomic number, (ex: hydrogen has one proton, it’s atomic number is 1)

Question 30

Look at the periodic table. How can you determine the number of electron shells in each atom? What about the number of electrons in their valence shell?

Answer 30

The Y axis is labeled “Period” and has the rows numbered 1-7, this is how you can determine the number of electron shells. (ex: Hydrogen and Helium have 1 electron shell; Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, and Neon have 2 electron shells.

The X axis is labeled “Main-Group Elements” and has the columns numbered 1-8, this is how you determine the number of electrons in their valence shell. (ex: Hydrogen, Lithium, and Sodium have 1 electron in their valence shell; Beryllium, Magnesium and Calcium have 2 electrons in their valence (outer) shell.

Question 31

The amount of solute dissolved in a given volume of solution is called the solution’s what?

Answer 31

concentration

Question 32

Magnesium has an atomic mass of 24. How is this statement true?

Answer 32

Magnesium has 12 protons and 12 neutrons, this is added together and 24 becomes the atomic mass.

Question 33

Van der Waals forces arise when…

Answer 33

random electron movement creates short-lived attractions

Question 34

T or F: Atoms are less stable when the valence shell is full.

Answer 34

False; they are MORE stable.

Question 35

T or F: Individually, H bonds are weak; collectively, many H bonds can be strong

Answer 35

TRUE.

Question 36

T or F: Van der Waals dispersion forces are stronger than hydrogen bonds

Answer 36

FALSE: they are weaker.

Question 37

Why is the atomic mass of an element slightly greater than its predicted mass?

Answer 37

Because of the presence of a small amount of heavier isotopes.

Question 38

The most abundant element in living organisms is?

Answer 38

oxygen

Question 39

T or F: Ice is denser than liquid water at all temperatures.

Answer 39

FALSE; Ice is less dense than water because the hydrogen bonds are more spaced apart which lowers the density.